Organic electroluminescent element

ABSTRACT

Provided is an organic EL element which is low voltage and has practical use utility while exhibiting high light emission efficiency and drive stability. Thus, an organic electroluminescent element obtained by layering a positive electrode, an organic layer and a negative electrode on a substrate, wherein at least one layer among the organic layers contains (i) a carbazole compound represented by general formula (1), and (ii) a carborane compound having one or more divalent carborane compounds and an aromatic group substituted for a carborane compound. Herein, L 1  is an aromatic hydrocarbon group, an aromatic heterocyclic group, or a linked aromatic group configured by linking 2-6 of said aromatic rings, p is an integer of 1-3, and m is an integer of 2-4.

FIELD

The present invention relates to an organic electroluminescent device(hereinafter, referred to as “organic EL device”) and in particularrelates to an organic EL device having an organic layer comprising aplurality of compounds.

BACKGROUND

When a voltage is applied to an organic EL device, a hole is injectedfrom an anode into a light-emitting layer, and an electron is injectedfrom a cathode into the layer. Then, in the light-emitting layer, thehole and the electron thus injected recombine to produce an exciton. Atthis time, according to the statistical law of electron spins, singletexcitons and triplet excitons are produced at a ratio of 1:3. Theinternal quantum efficiency of a fluorescent emission-type organic ELdevice using light emission by a singlet exciton is said to be at most25%. Meanwhile, it has been known that the internal quantum efficiencyof a phosphorescent emission-type organic EL device using light emissionby a triplet exciton can be improved to 100% when intersystem crossingfrom a singlet exciton is efficiently performed.

Recently, highly efficient organic EL devices utilizing delayedfluorescence have been developed. For example, Patent Literature 1discloses an organic EL device utilizing a TTF (Triplet-Triplet Fusion)mechanism, which is one type of mechanism of delayed fluorescence.Patent Literature 2 discloses an organic EL device utilizing TADF(Thermally Activated Delayed Fluorescence). Though both are meanscapable of enhancing internal quantum efficiency, a further improvementin lifetime characteristics has been demanded in the same manner as forphosphorescent emission-type devices.

CITATION LIST Patent Literature

-   Patent Literature 1: WO2010/134350 A1-   Patent Literature 2: WO2011/070963 A1-   Patent Literature 3: JP 2005-162709 A-   Patent Literature 4: JP 2005-166574 A-   Patent Literature 5: US2012/0319088 A1-   Patent Literature 6: WO2013/094834 A1-   Patent Literature 7: US2009/0167162 A1-   Patent Literature 8: WO2015/137202 A1

Patent Literature 3 to 8 disclose the use of a carborane compound as ahost material. Patent Literature 8 discloses the use of a specificcarborane compound as a delayed fluorescent material, the use ofbiscarbazole compounds as delayed fluorescent materials, and the use ofa carborane compound as a host material in a light-emitting layer, butdoes not teach the use of a carborane compound mixed with a carbazolecompound in an organic layer other than a light-emitting layer or as ahost material in a light-emitting layer.

SUMMARY Technical Problem

In order to apply an organic EL device to a display device, such as aflat panel display, or a light source, the luminous efficiency of thedevice needs to be improved, and at the same time, stability at the timeof driving needs to be sufficiently secured. In view of theabove-mentioned present circumstances, an object of the presentinvention is to provide a practically useful organic EL device havinghigh efficiency and high driving stability while having a low drivingvoltage.

Solution to Problem

The present invention relates to an organic electroluminescent devicecomprising a substrate having stacked thereon an anode, an organic layerand a cathode, wherein at least one layer of the organic layer comprises(i) a compound represented by the following general formula (1) and (ii)a compound represented by the following general formula (2):

In general formula (1), L¹ is a p-valent group, and is a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted heteroaromatic ring group having 3 to 30carbon atoms, or a substituted or unsubstituted linked aromatic groupformed by linking 2 to 6 of the aromatic rings thereof (which refer toaromatic rings of the substituted or unsubstituted aromatic hydrocarbongroup or substituted or the unsubstituted aromatic heterocyclic group).

Each R independently represents hydrogen, a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted orunsubstituted heteroaromatic ring group having 3 to 30 carbon atoms, asubstituted or unsubstituted linked aromatic group formed by linking 2to 6 of the rings thereof an alkyl group having 1 to 12 carbon atoms, adiarylamino group having 12 to 44 carbon atoms, a cyano group, a nitrogroup, or a fluoro group. The alkyl group may be linear, branched, orcyclic.

p is a substitution number, and represents an integer of 1 to 3. m is arepeating number, and independently represents an integer of 2 to 4.

When L¹ or R is a heteroaromatic ring group, the heteroaromatic ringgroup is not a carbazolyl group or a carbazole ring-containing group.

In general formula (2), ring A be a divalent carborane group of C₂B₁₀H₁₀represented by formula (a1) or formula (b1). However, when a pluralityof rings A are present in a molecule, the plurality of rings A may bethe same or different from each other. q is a substitution number, andrepresents an integer of 1 to 4. n is a repeating number, andindependently represents an integer of 0 to 2.

L² represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 carbon atoms, a substituted or unsubstitutedheteroaromatic ring group having 3 to 30 carbon atoms, or a substitutedor unsubstituted linked monovalent aromatic group formed by linking 2 to6 aromatic rings thereof.

L³ is a single bond or a (q+1)-valent group, and represents asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 30carbon atoms, a substituted or unsubstituted heteroaromatic ring grouphaving 3 to 30 carbon atoms, or a substituted or unsubstituted linkedaromatic group formed by linking 2 to 6 aromatic rings thereof. However,when q=1 and n=1, L³ represents a single bond, an aromatic heterocyclicgroup, or a linked aromatic group comprising at least one aromaticheterocyclic group.

L⁴ is independently a single bond or divalent group. The divalent grouprepresents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 carbon atoms, a substituted or unsubstitutedheteroaromatic ring group having 3 to 30 carbon atoms, or a substitutedor unsubstituted linked aromatic group formed by linking 2 to 6 of thesubstituted or unsubstituted aromatic rings.

In general formula (1), p is an integer of 1 or 2 and m is independentlyan integer of 2 or 3. It is preferable that all binding structuresbetween carbazolyl groups are binding structures represented by formula(d1) or binding structures represented by formula (c1) and formula (d1).The latter binding structures are more preferable.

In general formula (1), L¹ is preferably a p-valent group formed byremoving p hydrogen atoms from any one of formulae (3) to (6), and ismore preferably a p-valent group formed by removing p hydrogen atomsfrom any one of formulae (3), (4), and (5).

In formulae (3) to (6), each X independently represents CH or nitrogen,each R′ independently represents hydrogen, a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted heteroaromatic ring group having 3 to 30carbon atoms, an alkyl group having 1 to 12 carbon atoms, a diarylaminogroup having 12 to 44 carbon atoms, a cyano group, a nitro group, or afluoro group. In formulae (4) and (6), Y represents oxygen or sulfur,and in formulae (5), r represents an integer of 0 to 2.

In general formula (1), the total of m can be an integer of 2 to 6.

In general formula (2), it is preferable that ring A be a divalentcarborane group of C₂B₁₀H₁₀ represented by formula (a1), the aromaticrings of L² and L³, which bond to ring A, be the same, or L² and L³ be asubstituted or unsubstituted dibenzofuranyl group or a substituted orunsubstituted dibenzothiophenyl group.

The organic layer comprising a compound represented by the followinggeneral formula (1) and a compound represented by the following generalformula (2) is preferably at least one layer selected from alight-emitting layer containing a luminescent dopant, anelectron-blocking layer, and a hole-blocking layer. It is morepreferable that the organic layer comprising two or more compounds be alight-emitting layer containing a luminescent dopant and contain the twocompounds as host materials.

Further, the luminescent dopant is preferably a delayed fluorescentdopant or an organometallic complex comprising at least one metalselected from ruthenium, rhodium, palladium, silver, rhenium, osmium,iridium, platinum, and gold.

In order to improve the characteristics of the devices, it is importantto prevent the leakage of excitons and charge into adjacent layers.Improving deviation of light emitting areas in a light-emitting layer iseffective to prevent such leakage of charge/excitons. For this purpose,it is necessary to control the injection/transportation amount of bothtypes of charge (electron/hole) in a material constituting an organiclayer to within a preferable range.

Regarding a carbazole compound represented by general formula (1), thestability of the skeleton thereof is high, and the electron/holeinjection/transportation property thereof can be controlled using anisomer or a substituent to some extent. However, it is difficult tocontrol the injection/transportation amount of both types of thecompound alone to a preferable range. Regarding a carborane compoundrepresented by general formula (2), the lowest unoccupied molecularorbital (LUMO), which influences the electron injection/transportationproperty, is widely distributed throughout the molecule thereof, andthus, the electron injection/transportation property of a device ishighly controllable. Additionally, since the skeleton stability is highin the same manner as the carbazole compound, the charge injectionamount into an organic layer can be precisely controlled by the use ofthe carborane compound mixed with a biscarbazole compound. Inparticular, by the use thereof in a light-emitting layer or a chargeblocking layer, the balance of both types of charges can be controlled.In the cases of delayed fluorescent EL devices and phosphorescent ELdevices, since each of the compounds has excitation energy (singlet andtriplet) high enough to confine excitation energy generated in alight-emitting layer, there is no energy outflow from inside thelight-emitting layer, and high efficiency and long life can be achievedat low voltages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates the cross-section of an example of anorganic EL device.

DESCRIPTION OF EMBODIMENTS

The organic electroluminescent device of the present invention,comprising a substrate having stacked thereon an anode, an organiclayer, and a cathode, comprises (i) a compound represented by generalformula (1) and (ii) a compound represented by general formula (2) in atleast one layer of the organic layer. The compounds of general formula(1) and general formula (2) each may be one compound, or both or eitherone may be two or more compounds. These compounds are present as amixture in the organic layer. The ratio of the compound represented bygeneral formula (1) is desirably 30 wt % or more with respect to thetotal of the compound represented by general formula (1) and thecompound represented by general formula (2). This ratio is morepreferably 35 to 95 wt %, and further preferably 40 to 90 wt %.

In general formula (1), L¹ is a p-valent aromatic group. The aromaticgroup refers to an aromatic hydrocarbon group, an aromatic heterocyclicgroup, or a linked aromatic group formed by linking 2 to 6 of thearomatic rings thereof. The aromatic ring refers to aromatic hydrocarbonrings, heteroaromatic rings, or both.

The p-valent aromatic hydrocarbon group is a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms.The aromatic heterocyclic group is a substituted or unsubstitutedaromatic heterocyclic group having 3 to 30 carbon atoms. The linkedaromatic group is a linked aromatic group formed by linking 2 to 6aromatic rings of the aromatic hydrocarbon group and the aromaticheterocyclic group via direct bonding, and is a substituted orunsubstituted linked aromatic group. The p-valent aromatic hydrocarbongroup is preferably a substituted or unsubstituted aromatic hydrocarbongroup having 6 to 18 carbon atoms, an aromatic heterocyclic group otherthan a substituted or unsubstituted carbazolyl group having 3 to 17carbon atoms, or a substituted or unsubstituted linked aromatic groupformed by linking 2 to 4 of the rings thereof.

In general formula (1), each R independently represents hydrogen, asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 30carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 30 carbon atoms, a substituted or unsubstituted linkedaromatic group formed by linking 2 to 6 of the rings thereof an alkylgroup having 1 to 12 carbon atoms, a diarylamino group having 12 to 44carbon atoms, a cyano group, a nitro group, or a fluoro group. Each Rpreferably is a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, a substituted or unsubstituted aromaticheterocyclic group having 3 to 17 carbon atoms, or a substituted orunsubstituted linked aromatic group formed by linking 2 to 4 of therings thereof. The alkyl group may be linear, branched, or cyclic.

When L¹ or R is an aromatic heterocyclic group, the aromaticheterocyclic group does not comprise a carbazolyl group. The carbazolylgroup is understood to encompass typical carbazolyl groups, divalent orhigher valent carbazolyl groups, and carbazole ring-containing groupswhich may have a substituent.

When L¹ and R in general formula (1), (c1), and (d1) are anunsubstituted aromatic hydrocarbon group, an aromatic heterocyclic groupother than an unsubstituted carbazolyl group, or an unsubstituted linkedaromatic group, specific examples thereof include p-valent or monovalentgroups formed by removing hydrogen from benzene, pentalene, indene,naphthalene, azulene, heptalene, octalene, indacene, acenaphthylene,phenalene, phenanthrene, anthracene, trindene, fluoranthene,acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene,tetraphene, tetracene, pleiadene, picene, perylene, pentaphene,pentacene, tetraphenylene, cholanthrylene, helicene, hexaphene,rubicene, coronene, trinaphthylene, heptaphene, pyranthrene, and otheraromatic hydrocarbon compounds, furan, benzofuran, isobenzofuran,xanthene, oxanthrene, dibenzofuran, peri-xanthenoxanthene, thiophene,thioxanthene, thianthrene, phenoxathiin, thionaphthene,isothianaphthene, thiophthene, thiophanthrene, dibenzothiophene,pyrrole, pyrazole, tellurazole, selenazole, thiazole, isothiazole,oxazole, furazan, pyridine, pyrazine, pyrimidine, pyridazine, triazine,indolizine, indole, isoindole, indazole, purine, quinolizine,isoquinoline, imidazole, naphthyridine, phthalazine, quinazoline,benzodiazepine, quinoxaline, cinnoline, quinoline, pteridine,phenanthridine, acridine, perimidine, phenanthroline, phenazine,carboline, phenotellurazine, phenoselenazine, phenothiazine,phenoxazine, anthyridine, benzothiazole, benzimidazole, benzoxazole,benzisooxazole, benzisothiazole, and other heteroaromatic ringcompounds, and aromatic compounds each composed of a plurality of linkedaromatic groups of the above aromatic compounds

In the case of a linked aromatic group formed by linking a plurality oflinked aromatic groups, the number of linked groups is 2 to 6,preferably 2 to 4. The linked aromatic groups may be the same ordifferent.

Specific examples of the linked aromatic group include p-valent ormonovalent groups formed by removing hydrogen from biphenyl, terphenyl,quaterphenyl, bipyridine, bipyrimidine, bitriazine, terpyridine,bistriazylbenzene, binaphthalene, phenylpyridine, diphenylpyridine,triphenylpyridine, phenylpyrimidine, diphenylpyrimidine,triphenylpyrimidine, phenyltriazine, diphenyltriazine,triphenyltriazine, phenylnaphthalene, diphenylnaphthalene,phenyldibenzofuran, phenyldibenzothiophene, dibenzofuranylpyridine,dibenzothiophenylpyridine, and other aromatic compounds.

When the aromatic hydrocarbon group, aromatic heterocyclic group, orlinked aromatic group has a substituent, the substituent may be selectedfrom an alkyl group having 1 to 20 carbon atoms, an aralkyl group having7 to 38 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, analkynyl group having 2 to 20 carbon atoms, a dialkylamino group having 2to 40 carbon atoms, a diarylamino group having 12 to 44 carbon atoms, adiaralkylamino group having 14 to 76 carbon atoms, an acyl group having2 to 20 carbon atoms, an acyloxy group having 2 to 20 carbon atoms, analkoxy group having 1 to 20 carbon atoms, an alkoxycarbonyl group having2 to 20 carbon atoms, an alkoxycarbonyloxy group having 2 to 20 carbonatoms, an alkylsulfonyl group 1 to 20 having carbon atoms, a cyanogroup, a nitro group, a fluoro group, and a tosyl group. The substituentis preferably selected from an alkyl group having 1 to 12 carbon atoms,an aralkyl group having 7 to 20 carbon atoms, a diarylamino group having12 to 30 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, acyano group, a fluoro group, and a tosyl group. The alkyl group may belinear, branched, or cyclic.

Specific examples of the substituent include methyl, ethyl, propyl,butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl, icosyl, and other alkyl groups,phenylmethyl, phenylethyl, phenylicosyl, naphthylmethyl,anthranilmethyl, phenanthrenylmethyl, pyrenymethyl, and other aralkylgroups, vinyl, propenyl, butenyl, pentenyl, decenyl, icosenyl, and otheralkenyl groups, ethynyl, propargyl, butynyl, pentynyl, decynyl,icosynyl, and other alkynyl groups, dimethylamino, ethylmethylamino,diethylamino, dipropylamino, dibutylamino, dipentynylamino,didecylamino, diicosylamino, and other dialkylamino groups,diphenylamino, naphthylphenylamino, dinaphthylamino, dianthranylamino,diphenanthrenylamino, dipyrenylamino, and other diarylamino groups,diphenylmethylamino, diphenylethylamino, phenylmethylphenylethylamino,dinaphthyhnethylamino, dianthranilmethylamino,diphenanthrenylmethylamino, and other diaralkylamino groups, acetyl,propionyl, butyryl, valeryl, benzoyl, and other acyl groups, acetyloxy,propionyloxy, butyryloxy, valeryloxy, benzoyloxy, and other acyloxygroups, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy,octoxy, nonyloxy, decanyloxy, and other alkoxy groups, methoxycarbonyl,ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, andother akoxycarbonyl groups, methoxycarbonyloxy, ethoxycarbonyloxy,propoxycarbonyloxy, butoxycarbonyloxy, pentoxycarbonyloxy, and otherakoxycarbonyloxy groups, methylsulfonyl, ethylsulfonyl, propylsulfonyl,butylsulfonyl, pentylsulfonyl, and other alkyl sulfoxy groups, cyanogroup, nitro group, fluoro group, and a tosyl group. The substituent ispreferably selected from methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, octyl, nonyl, decyl, and other alkyl groups having 1 to 12carbon atoms, phenylmethyl, phenylethyl, naphthylmethyl,anthranilmethyl, phenanthrenylmethyl, pyrenymethyl, and other aralkylgroups having 7 to 20 carbon atoms, methoxy, ethoxy, propoxy, butoxy,pentoxy, hexoxy, heptoxy, octoxy, nonyloxy, decanyloxy, and other alkoxygroups having 1 to 10 carbon atoms, diphenylamino, naphthylphenylamino,dinaphthylamino, dianthranylamino, diphenanthrenylamino, and otherdiarylamino groups having two aromatic hydrocarbon groups having 6 to 15carbon atoms, cyano group, fluoro group, and tosyl group.

As used herein, the term “linked aromatic group” refers to a groupcomposed of a plurality of linked single rings or aromatic rings(aromatic hydrocarbon rings, heteroaromatic rings, or both) of aromaticcompounds of condensed ring structures. The linked aromatic groups referto linked aromatic rings of aromatic groups via direct bonds. When thearomatic groups are substituted aromatic groups, no substituents arearomatic groups.

The linked aromatic groups may be linear or branched. The aromatic ringsto be linked may be the same or different, may have either or both of anaromatic hydrocarbon ring and a heteroaromatic ring, and may have asubstituent.

Herein, the number of carbon atoms calculated is understood to excludethe number of carbon atoms of substituents. However, it is preferablethat the total number of carbon atoms including the carbon atoms of thesubstituents be within the above ranges of the number of carbon atoms.The number of carbon atoms of the linked aromatic groups is understoodto be the total number of carbon atoms of linked aromatic hydrocarbongroups and aromatic heterocyclic groups.

When the linked aromatic group is a monovalent group, the linking frommay be, for example, as follows:

When the linked aromatic group is a divalent group, the linking from maybe, for example, as follows. When the linked aromatic group is atrivalent or higher valent group, the linking from can be understoodfrom the above.

In formulae (7) to (12), Ar¹¹ to Ar¹⁶ and Ar²¹ to Ar²⁶ representsubstituted or unsubstituted aromatic rings (aromatic groups), andring-forming atoms of the aromatic groups bond together via directbonding. The bonds start from the ring-forming atoms of the aromaticgroups. The aromatic rings (aromatic groups) refer to aromatichydrocarbon groups or aromatic heterocyclic groups, and may bemonovalent or higher valent groups.

In formulae (7) to (12), the bond starts from Ar¹¹, Ar²¹, or Ar²³, butcan start from another aromatic ring. In the case of divalent or highervalent group, two or more bonds start from one aromatic group.

When R in general formula (1), (c1), and (d1) is an alkyl group having 1to 12 carbon atoms or an diarylamino group having 12 to 44 carbon atoms,specific examples thereof include methyl, ethyl, propyl, butyl,tert-butyl, pentyl, isopentyl, cyclopentyl, hexyl, cyclohexyl, heptyl,octyl, nonyl, decyl, undecyl, dodecyl, cyclohexyl, and other alkylgroups, diphenylamino, naphthylphenylamino, dinaphthylamino,dianthranylamino, diphenanthrenylamin, and other diarylamino groups.

In general formula (1), preferable embodiments of L¹ include p-valentgroups formed from aromatic compounds of formulae (3) to (6), preferablyformulae (3), (4), and (6). The p-valent groups having a valence isformed by removing p hydrogen atoms from carbon atoms forming rings informulae (3) to (6). When p is 2 or more, hydrogen atoms may be removedfrom the same ring or different rings.

In formulae (3) to (6), each X independently represents methine ornitrogen. Among Xs which form six-membered rings, 0 to 3 Xs arepreferably nitrogen. More preferably, all Xs are methine. In formulae(4) and (6). Y represents oxygen or sulfur. In formula (5), r representsan integer of 0 to 2, and is preferably 0 or 1.

In formulae (3) to (6), each R′ is independently hydrogen, a substitutedor unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms,a substituted or unsubstituted heteroaromatic ring group having 3 to 30carbon atoms, an alkyl group having 1 to 12 carbon atoms, a diarylaminogroup having 12 to 44 carbon atoms, a cyano group, a nitro group, or afluoro group. Each R′ is preferably hydrogen, a substituted orunsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, ora substituted or unsubstituted heteroaromatic ring group having 3 to 17carbon atoms.

R′ is the same as R in general formula (1) except that theheteroaromatic ring group comprises a carbazolyl group, and does notcomprise a linked aromatic group.

In general formula (1), p represents an integer of 1 to 3. p ispreferably 1 or 2, and more preferably 1.

In general formula (1), each m independently represents an integer of 2to 4. m is preferably 2 or 3.

When m is 2 or more, there is a structure of a carbazolyl group directlybonded to a carbazolyl group. Preferably, in the formula, at least onebinding structure represented by formula (d1) is present. It ispreferable that all binding structures between carbazolyl groups berepresented by only formula (d1) or only both of formula (c1) andformula (d1). It is more preferable that all binding structures betweencarbazolyl groups be represented by only both of formula (c1) andformula (d1). The carbazolyl group as used herein refers to a condensedring of three rings in general formula (1). The total number of m (thetotal number of carbazolyl groups) is an integer of 2 to 12, preferably2 to 9, and more preferably 2 to 6.

Preferable examples of the compound represented by general formula (1)are shown below, but the compound is not limited thereto.

Next, the compound represented by general formula (2) (carboranecompound) will be described. Ring A represents a divalent carboranegroup of C₂B₁₀H₁₀ represented by formula (a1) or formula (b1). Aplurality of rings A in a molecule may be the same or different. It ispreferable that all of rings A are carborane groups represented byformula (a1).

Two bonds of the divalent carborane group may start from C or B, but thebond to L² or L³ preferably starts from C.

n is a repeating number and represents an integer of 0 to 2. n ispreferably 0 or 1, and more preferably 0.

q is a substitution number and represents an integer of 1 to 4. q ispreferably an integer of 1 or 2, and is more preferably 1.

L² is a substituted or unsubstituted aromatic hydrocarbon group having 6to 30 carbon atoms, a substituted or unsubstituted aromatic heterocyclicgroup having 3 to 30 carbon atoms, or a substituted or unsubstitutedlinked aromatic group formed by linking 2 to 6 of the rings thereof. L²is preferably a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, a substituted or unsubstituted aromaticheterocyclic group having 3 to 17 carbon atoms, or a substituted orunsubstituted linked aromatic group formed by linking 2 to 4 of thearomatic rings thereof.

L³ is a single bond or a (q+1)-valent group which is a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or a substituted or unsubstituted linked aromatic groupformed by linking 2 to 6 of the aromatic rings thereof. L³ is preferablya single bond, a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, a substituted or unsubstituted aromaticheterocyclic group having 3 to 17 carbon atoms, or a substituted orunsubstituted linked aromatic group formed by linking 2 to 4 of thearomatic rings thereof. However, when q=1 and n=1, L³ represents asingle bond, an aromatic heterocyclic group, or a linked aromatic groupcomprising at least one aromatic heterocyclic group.

L⁴ independently represents a single bond or a divalent group. Thedivalent group is a substituted or unsubstituted aromatic hydrocarbongroup having 6 to 30 carbon atoms, a substituted or unsubstitutedaromatic heterocyclic group having 3 to 30 carbon atoms, or asubstituted or unsubstituted linked aromatic group formed by linking 2to 6 of the aromatic rings thereof. L⁴ is preferably a single bond, asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 18carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 17 carbon atoms, or substituted or unsubstituted linkedaromatic group formed by linking 2 to 4 of the aromatic rings thereof.

When L², L³, and L⁴ in general formula (2) are an aromatic hydrocarbongroup, an aromatic heterocyclic group, or a linked aromatic group formedby linking 2 or 6 of the aromatic rings, L², L³, or L⁴ is the same asdescribed above regarding L¹ and R in general formula (1) except that acarbazolyl group is not excluded from the aromatic heterocyclic group.However, when q=1 and n=1, L³ represents a single bond, an aromaticheterocyclic group, or a linked aromatic group comprising at least onearomatic heterocyclic group.

When n=0, it is preferable that L³ and L² be the same or aromatic ringsof L³ and L², which bond to ring A, be the same. That the aromatic ringswhich bond to ring A are the same means that Ar² and Ar⁴, which bond toring A, are the same when L represents Ar¹—Ar²— and L² represents—Ar³—Ar⁴—. Ar¹ to Ar⁴ are each an aromatic ring which may have asubstituent. When n=0, it is preferable that L²=L³-(H)q.

Preferable examples of the compound represented by general formula (2)are shown below, but the compound is not limited thereto.

The organic EL device of the present invention comprises a mixture of acompound represented by general formula (1) and a compound representedby general formula (2) in at least one organic layer of the organic ELdevice. Since the mixture is excellent in charge transporting property,the mixture may be used in any organic layer. The mixture is preferablycontained in a light-emitting layer, an electron-transporting layer, ora hole-blocking layer, and more preferably in a light-emitting layer.

When the mixture is used in a light-emitting layer, the mixture may beused as a luminescent dopant material, but is preferably used as a hostmaterial while another luminescent dopant material, a fluorescent dopantmaterial, or a thermally-activated delayed fluorescent dopant materialis used as the luminescent dopant material. In particular, anorganometallic complex comprising at least one metal selected fromruthenium, rhodium, palladium, silver, rhenium, osmium, iridium,platinum and gold is a preferable embodiment of the luminescent dopantmaterial.

The mixture may be mixed prior to forming the device and be depositedusing a deposition source, or may be mixed by an operation, such asco-deposition using a plurality of deposition sources, at the time offorming the device.

The mixture may be used by forming a film on a substrate or the likeusing a wet process, such as spin coating or ink-jetting, without usinga dry process with a deposition source.

Next, the structure of the organic EL device of the present inventionwill be described referring the drawing, but the structure of theorganic EL device of the present invention is not limited to thatillustrated in the drawing.

(1) Configuration of Organic EL Device

FIG. 1 schematically shows the cross section of an example of an organicEL device generally used in this invention and 1 represents a substrate,2 an anode, 3 a hole-injecting layer, 4 a hole-transporting layer, 5 alight-emitting layer, 6 an electron-transporting layer, 7 anelectron-injecting layer, and 8 a cathode. The organic EL device of thisinvention comprises the anode, the light-emitting layer, theelectron-transporting layer, and the cathode as essential layers andother layers may be provided as needed. Such other layers are, forexample, a hole-injecting/transporting layer, an electron-blockinglayer, and a hole-blocking layer, but are not limited thereto. The term“hole-injecting/transporting layer” means a hole-injecting layer and/ora hole-transporting layer.

(2) Substrate

The substrate 1 serves as a support for an organic electroluminescentdevice and the materials useful therefor include a quartz plate, a glassplate, a metal sheet, a metal foil, a plastic film, and a plastic sheet.In particular, a glass plate and a flat, transparent sheet of syntheticresin such as polyester, polymethacrylate, polycarbonate, andpolysulfone are preferred. In the case where a synthetic resin substrateis used, the gas barrier property of the resin needs to be taken intoconsideration. When the gas barrier property of the substrate is toolow, the air passing through the substrate may undesirably deterioratethe organic electroluminescent device. One of the preferred methods forsecuring the gas barrier property is to provide a dense silicon oxidefilm or the like at least on one side of the synthetic resin substrate.

(3) Anode

The anode 2 is provided on the substrate 1 and plays a role of injectingholes into the hole-transporting layer. The anode is usually constructedof a metal such as aluminum, gold, silver, nickel, palladium, andplatinum, a metal oxide such as an oxide of indium and/or tin and anoxide of indium and/or zinc, a metal halide such as copper iodide,carbon black, and an electrically conductive polymer such aspoly(3-methylthiophene), polypyrrole, and polyaniline. The anode isformed mostly by a process such as sputtering and vacuum deposition. Inthe case where silver or any other metal, copper iodide, carbon black,an electrically conductive metal oxide, or an electrically conductivepolymer is available in fine particles, the anode can be formed bydispersing the particles in a solution of a suitable binder resin andcoating the substrate with the dispersion. Further, in the case of anelectrically conductive polymer, the anode can be formed as a thin filmby performing electrolytic polymerization of the corresponding monomerdirectly on the substrate 1 or by coating the substrate with thepolymer. The anode may also be formed by stacking different materialsone upon another. The thickness of the anode varies with the requirementfor transparency. In applications where transparency is required, it isdesirable to control the transmission of visible light normally at 60%or more, preferably at 80% or more. In this case, the thickness becomesnormally 5 to 1,000 nm, preferably 10 to 500 nm. In applications whereopaqueness is accepted, the anode may be the same in transmission as thesubstrate. Furthermore, a different electrically conductive material canbe stacked on the aforementioned anode.

(4) Hole-Transporting Layer

The hole-transporting layer 4 is provided on the anode 2 and thehole-injecting layer 3 may be disposed between the two. The conditionthat the material of choice for the hole-transporting layer must satisfyis an ability to inject holes from the anode at high efficiency andtransport the injected holes efficiently. This makes it necessary forthe material to satisfy the following requirements; low ionizationpotential, high transparency against visible light, high hole mobility,good stability, and low inclination to generate impurities that becometraps of holes during fabrication and use. Further, since thehole-transporting layer is arranged in contact with the light-emittinglayer 5, the material for the hole-transporting layer must not lower theefficiency by quenching light emitted from the light-emitting layer orforming exciplexes with the light-emitting layer. Besides theaforementioned general requirements, heat resistance is required forapplications such as vehicle-mounted display devices. Hence, thematerial desirably has a Tg of 85° C. or higher.

A mixture of general formula (1) and general formula (2) may be used asthe hole-transporting material, or any of the compounds known thus faras hole-transporting materials may be used as such according to thisinvention. Examples include aromatic diamines containing two or moretertiary amines whose nitrogen atoms are substituted with two or morecondensed aromatic rings, starburst aromatic amines such as4,4′,4″-tris(1-naphthylphenylamino)triphenylamine, an aromatic amineconsisting of a tetramer of triphenylamine, and Spiro compounds such as2,2′,7,7′-tetrakis(diphenylamino)-9,9′-spirobifluorene. These compoundsmay be used alone or as a mixture if necessary.

In addition to the aforementioned compounds, examples of thehole-transporting materials include polymeric materials such aspolyvinylcarbazole, polyvinyltriphenylamine, and polyaryleneethersulfonecontaining tetraphenylbenzidine.

When a coating process is used for forming the hole-transporting layer,a coating solution is prepared from one kind or two kinds or more ofhole-transporting materials of choice and, if necessary, a binder resinwhich does not become a trap of holes and an additive such as animprover of coating properties are applied to the anode by a processsuch as spin coating, and dried to form the hole-transporting layer.Examples of the binder resin include polycarbonate, polyarylate, andpolyester. As a binder resin lowers the hole mobility when added in alarge amount, the binder is preferably added in a small amount, usually50 wt % or less.

When a vacuum deposition process is used for forming thehole-transporting layer, the hole-transporting material of choice isintroduced to a crucible placed in a vacuum container, the container isevacuated to 1×10⁻⁴ Pa or so by a suitable vacuum pump, the crucible isheated to evaporate the hole-transporting material, and the vapor isdeposited on the substrate that has an anode formed thereon and isplaced opposite the crucible to form the hole-transporting layer. Thethickness of the hole-transporting layer is normally 1 to 300 nm,preferably 5 to 100 nm. The vacuum deposition process is generally usedto form such a thin film uniformly.

(5) Hole-Injecting Layer

For the purpose of still further enhancing the hole-injecting efficiencyand improving the adhesive strength of the organic layer to the anode asa whole, the hole-injecting layer 3 is disposed between thehole-transporting layer 4 and the anode 2. Disposition of thehole-injecting layer produces an effect of lowering the driving voltageof the device in the initial period and, at the same time, suppressing arise in voltage during continuous driving of the device at constantcurrent density. The hole-injecting material of choice must satisfy thefollowing requirements; it is formable into a thin film that is uniformin quality and makes good contact with the anode, and it is thermallystable. Namely, the material is required to have a high glass transitionwhich is 100° C. or above. Further, the material is required to have alow ionization potential to facilitate injection of holes from the anodeand exhibit high hole mobility.

For this purpose, a mixture of general formula (1) and general formula(2) may be used or any of the compounds known thus far, such asphthalocyanine compounds such as copper phthalocyanine; organiccompounds such as polyaniline and polythiophene; sputtered carbonmembranes; metal oxides such as vanadium oxide, ruthenium oxide, andmolybdenum oxide; and p-type organic compounds such as1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) andhexanitrilehexaazatriphenylene (HAT), may be used alone or mixed asneeded. The hole-injecting layer can also be formed as a thin film, likethe hole-transporting layer, and in the case where the material ofchoice is an inorganic compound, a process such as sputtering, electronbeam deposition, or plasma CVD can be used. The thickness of thehole-injecting layer formed as described above is normally 1 to 300 nm,preferably 5 to 100 nm.

(6) Light-Emitting Layer

The light-emitting layer 5 is provided on the hole-transporting layer 4.The light-emitting layer may be composed of a single light-emittinglayer or it may be constructed by stacking a plurality of light-emittinglayers one upon another. The light-emitting layer is composed of a hostmaterial and a luminescent dopant. The luminescent dopant may be afluorescent material, a delayed fluorescent material, or aphosphorescent material. A mixture of compounds of general formula (1)and general formula (2) may be used as the luminescent dopant, but ispreferably used as the host material.

In the case of the fluorescent organic EL device, materials to be addedto the host materials include derivatives of condensed ring compoundssuch as perylene and rubrene, quinacridone derivatives, Phenoxazone 660,DCM1, perinone, coumarin derivatives, pyrromethene (diazaindacene)derivatives, and cyanine dyes.

In the case of the phosphorescent organic EL device, examples of thedelayed fluorescent material in the light-emitting layer includecarborane derivatives, tin complexes, indolocarbazole derivatives,copper complexes, and carbazole derivatives. Specific examples includethe compounds described in the following Non-Patent Literature andPatent Literature, but the delayed fluorescent material is not limitedthereto.

-   1) Adv. Mater. 2009, 21, 4802-4806-   2) Appl. Phys. Lett. 98, 083302 (2011)-   3) JP 2011-213643 A-   4) J. Am. Chem. Soc. 2012, 134, 14706-14709

Specific examples of the delayed luminescent material are describedbelow, but the delayed luminescent material is not limited thereto.

When the delayed fluorescent material is used as the delayedfluorescence dopant and a host material is contained therein, thecontent of the delayed fluorescence dopant contained in thelight-emitting layer is 0.01 to 50 wt %, preferably 0.1 to 20 wt %, andmore preferably 0.01 to 10%.

In the case of a phosphorescent organic EL device, an organometalliccomplex comprising at least one metal selected from ruthenium, rhodium,palladium, silver, rhenium, osmium, iridium, platinum and gold ispreferable as the phosphorescent dopant. Specific examples of thephosphorescent dopant are described in the Patent Literature below, butthe phosphorescent dopant is not limited thereto. As the host material,a mixture comprising a compound represented by general formula (1) and acompound represented by general formula (2) is excellent.

WO 2009-073245 A1, WO 2009-046266 A1, WO 2007-095118 A1, WO 2008-156879A1, WO 2008-140657 A1, US 2008-261076 A1, JP 2008-542203 A, WO2008-054584 A1, JP 2008-505925 A, JP 2007-522126 A, JP 2004-506305 A, JP2006-513278 A, JP 2006-50596 A, WO 2006-046980 A1, WO 2005-113704 A1, US2005-260449 A1, US 2005-2260448 A1, US 2005-214576 A1, WO 2005-076380A1, etc.

Preferred examples of the phosphorescent light-emitting dopant includecomplexes such as Ir(PPy)₃, complexes such as Ir(bt)2.acac3, andcomplexes such as PtOEt3, the complexes each having a noble metal devicesuch as Ir as a central metal. Specific examples of those complexes areshown below, but the phosphorescent light-emitting dopant is not limitedto the compounds described below.

It is preferred that the content of the phosphorescent light-emittingdopant in the light-emitting layer be in the range of from 2 to 40 wt %,preferably from 5 to 30 wt %.

The thickness of the light-emitting layer, which is not particularlylimited, is typically from 1 to 300 nm, preferably from 5 to 100 nm, anda thin film serving as the layer is formed by the same method as thatfor the hole-transporting layer.

—Blocking Layer—

The blocking layer is capable of blocking electric charge (electrons orholes) and/or excitons present in the light-emitting layer fromdiffusing to the outside of the light-emitting layer. Theelectron-blocking layer may be disposed between the light-emitting layerand the hole-transporting layer and block electrons from passing throughthe light-emitting layer toward the hole-transporting layer. Similarly,the hole-blocking layer may be disposed between the light-emitting layerand the electron-transporting layer and block holes from passing throughthe light-emitting layer toward the electron-transporting layer. Theblocking layer may also be used to block excitons from diffusing to theoutside of the light-emitting layer. That is, the electron-blockinglayer and the hole-blocking layer may respectively have the function ofan exciton-blocking layer. The term “electron-blocking layer” or“hole-blocking layer” as used herein means that a layer comprises onelayer by itself having the function of a charge (electron or hole)blocking layer and an exciton-blocking layer.

—Hole-Blocking Layer—

The hole-blocking layer has the function of an electron transportinglayer in a broad sense. The hole-blocking layer has a function ofinhibiting holes from reaching the electron transporting layer whiletransporting electrons, and thereby enhances the recombinationprobability of electrons and holes in the light-emitting layer.

As the material for the hole-blocking layer, a mixture of generalformula (1) and general formula (2) is preferably used, and thematerials for the electron-transporting layer described later may beused. The thickness of the hole-blocking layer of the present inventionis preferably 3 to 100 nm and more preferably 5 to 30 nm.

—Electron-Blocking Layer—

The electron-blocking layer has the function of transporting holes in abroad sense. The electron-blocking layer has a function of inhibitingelectrons from reaching the hole transporting layer while transportingholes, and thereby enhances the recombination probability of electronsand holes in the light-emitting layer.

As the material for the electron-blocking layer, a mixture of generalformula (1) and general formula (2) is preferably used, and thematerials for the hole-transporting layer described later may be used.The thickness of the electron-blocking layer of the present invention ispreferably 3 to 100 nm and more preferably 5 to 30 nm.

—Exciton-Blocking Layer—

The exciton-blocking layer is a layer for inhibiting excitons generatedthrough the recombination of holes and electrons in the light-emittinglayer from being diffused to the charge transporting layer, andinserting the layer enables effective confinement of excitons in thelight-emitting layer, and thereby enhances the luminous efficacy of thedevice. The exciton-blocking layer may be inserted adjacent to thelight-emitting layer on any of the side of the anode and the side of thecathode, and on both the sides. Specifically, in the case where theexciton-blocking layer is present on the side of the anode, the layermay be inserted between the hole transporting layer and thelight-emitting layer and adjacent to the light-emitting layer, and inthe case where the layer is inserted on the side of the cathode, thelayer may be inserted between the light-emitting layer and the cathodeand adjacent to the light-emitting layer. Between the anode and theexciton-blocking layer that is adjacent to the light-emitting layer onthe side of the anode, a hole injection layer, an electron barrier layerand the like may be provided, and between the cathode and theexciton-blocking layer that is adjacent to the light-emitting layer onthe side of the cathode, an electron injection layer, an electrontransporting layer, a hole barrier layer and the like may be provided.

As the material for the exciton-blocking layer, a mixture of generalformula (1) and general formula (2) is preferably used, and any commonlyused material may be used.

Examples of known exciton-blocking materials that may be used hereininclude 1,3-dicarbazolylbenzene (mCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (III) (BAlq).

(7) Electron-Transporting Layer

For the purpose of enhancing the luminous efficiency of the devicefurther still, the electron-transporting layer 6 is disposed between thelight-emitting layer 5 and the cathode 8. As the electron-transportinglayer, an electron-transporting material which can smoothly injectelectrons from the cathode is preferable. A mixture of general formula(1) and general formula (2) may be used and any commonly used materialsmay be used. Examples of the electron-transporting material whichsatisfies such limitations include metal complexes such as Alq₃,10-hydroxybenzo[h]quinoline metal complexes, oxadiazole derivatives,distyrylbiphenyl derivatives, silole derivatives, 3- or 5-hydroxyflavonemetal complexes, benzoxazole metal complexes, benzothiazole metalcomplexes, trisbenzimidazolybenzene, quinoxaline compounds,phenanthroline derivatives,2-t-butyl-9,10-N,N′-dicyanoanthraquinonediimine, n-type hydrogenatedamorphous silicon carbide, n-type zinc sulfide, and n-type zincselenide.

The thickness of the electron-transporting layer is typically 1 to 300nm and is preferably 5 to 100 nm. The electron-transporting layer isformed on the light-emitting layer by coating or vacuum deposition as inthe case of the hole-transporting layer. The vacuum deposition processis usually employed.

(8) Cathode

The cathode 8 plays a role of injecting electrons into theelectron-transporting layer 6. The materials useful for the cathode maybe the same as the aforementioned materials for the anode 2. However, ametal having a low work function is desirable for efficient injection ofelectrons and a metal such as tin, magnesium, indium, calcium, aluminum,and silver or any of alloys thereof may be used. Specific examples areelectrodes made from alloys having a low work function such asmagnesium-silver alloys, magnesium-indium alloys, and aluminum-lithiumalloys.

The thickness of the cathode is usually the same as that of the anode.For the purpose of protecting the cathode made from a metal having a lowwork function, covering the cathode with a metal of high work functionthat is stable against the air improves the stability of the device. Ametal such as aluminum, silver, copper, nickel, chromium, gold, andplatinum is used for this purpose.

Further, disposition of the electron-injecting layer 7 in the form of anultrathin insulating film (0.1 to 5 nm) of LiF, MgF₂, Li₂O, or the likebetween the cathode 8 and the electron-transporting layer 6 is also aneffective method for enhancing the efficiency of the device.

It is possible to fabricate a device with a structure that is thereverse of the structure shown in FIG. 1; that is, the device isfabricated by stacking, on the substrate 1, the cathode 8, theelectron-injecting layer 7, the electron-transporting layer 6, thelight-emitting layer 5, the hole-transporting layer 4, thehole-injecting layer 3, and the anode 2 one upon another in this order.As described earlier, it is also possible to dispose the organic ELdevice of the present invention between two substrates at least one ofwhich is highly transparent. In this case of the reverse structure, itis also possible to add or omit a layer or layers as needed.

The organic EL device of this invention is applicable to a singledevice, a device with its structure arranged in array, or a device inwhich the anode and the cathode are arranged in an X-Y matrix. Accordingto this invention, a combination of the first electron-transportinglayer containing a compound of specified skeleton with the secondelectron-transporting layer containing an existing electron-transportingmaterial other than the compound of specified skeleton or a materialcomparable to the existing material provides an organic EL device thatcan perform at enhanced luminous efficiency with markedly improveddriving stability even at low voltage. The organic EL device thusobtained displays excellent performance when applied to full-color ormulticolor panels.

This invention will be described in more detail below with reference tothe Examples, but will not be limited thereto. This invention can bereduced to practice in various modes unless such practice exceeds thesubstance of this invention. The first host and compound A refer to acompound represented by represented by general formula (1), and thesecond host and compound B refer to a compound represented byrepresented by general formula (2).

Example 1

A thin film was laminated by a vacuum deposition method at a degree ofvacuum of 2.0×10⁻⁵ Pa on a glass substrate having formed thereon ananode comprising indium tin oxide (ITO) having a thickness of 70 nm.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 30 nm to serve as a hole-injecting layer on the ITO. Next,4,4-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) was formed into alayer having a thickness of 15 nm to serve as a hole-transporting layer.Next, compound 1-2 serving as a first host and compound 2-1 serving as asecond host for a light-emitting layer and an iridium complex[iridium(III) bis(4,6-di-fluorophenyl)-pyridinato-N,C2′]picolinate](FIrpic) serving as a blue phosphorescent material as a light-emittinglayer guest were co-deposited from different deposition sources onto thehole-transporting layer to form a light-emitting layer having athickness of 30 nm. At this time, a vapor deposition rate ratio amongthe first host, the second host, and FIrpic was 47:47:6 (by weight).Next, Alq₃ was formed into a layer having a thickness of 25 nm to serveas an electron-transporting layer. Further, lithium fluoride (LiF) wasformed into a layer having a thickness of 1.0 nm to serve as anelectron-injecting layer on the electron-transporting layer. Finally,aluminum (Al) was formed into a layer having a thickness of 70 nm toserve as an electrode on the electron-injecting layer. The resultingorganic EL device has a layer construction comprising theelectron-injecting layer added between the cathode and theelectron-transporting layer in the organic EL device illustrated in FIG.1.

An external power source was connected to the resultant organic ELdevice and a DC voltage was applied to the device. As a result, anemission spectrum having a local maximum wavelength of 475 nm wasobserved and it was found that light emission from FIrpic was obtained.Table 1 shows the properties of the produced organic EL device.

Examples 2 to 21

Organic EL devices were each produced in the same manner as in Example 1except that in Example 1, a compound shown in Table 1 was used as thefirst host of the light-emitting layer (Examples 2 to 7).

Organic EL devices were each produced in the same manner as in Examples1 to 7 except that Compound 2-18 or 2-29 shown in Table 1 was used asthe second host of the light-emitting layer (Examples 8 to 21).

An external power source was connected to each of the resultant organicEL devices and a DC voltage was applied to the device. As a result, anemission spectrum having a local maximum wavelength of 475 an wasobserved for each of the organic EL devices and it was found that lightemission from FIrpic was obtained. Table 1 shows the properties of eachof the produced organic EL devices.

Comparative Examples 1 to 10

Organic EL devices were each produced in the same manner as in Example 1except that in Example 1, a compound shown in Table 1 was used alone asthe light-emitting layer host. The host amount was set to the sameamount as the total of the first host and second host in Example 1, andthe guest amount was the same. A power source was connected to each ofthe resultant organic EL devices and a DC voltage was applied to thedevice. As a result, an emission spectrum having a local maximumwavelength of 475 nm was observed for each of the organic EL devices andit was found that light emission from FIrpic was obtained. Table 2 showsthe properties of the produced organic EL devices.

In Tables 1 and 2, the luminance, the voltage, and the luminous efficacyare values at a driving current of 2.5 mA/cm², and the luminancehalf-time is a value at an initial luminance of 1,000 cd/m². CompoundNo. is the number attached to the chemical formulae.

TABLE 1 1st host 2nd host Luminous Luminance compound compound LuminanceVoltage efficiency half-time Example No. No. (cd/m²) (V) (lm/W) (h) 11-2  2-1  610 5.3 14.5 1800 2 1-8  610 5.4 14.3 1800 3 1-11 610 5.3 14.51800 4 1-15 610 5.4 14.2 3000 5 1-44 620 5.5 14.1 2100 6 1-45 610 5.613.8 2700 7 1-68 620 6.3 12.3 2100 8 1-2  2-18 610 5.7 13.4 1620 9 1-8 610 5.8 13.3 1620 10 1-11 600 5.7 13.2 1620 11 1-15 610 5.8 13.1 2700 121-44 610 5.8 13.3 1890 13 1-45 600 6.1 12.4 2430 14 1-68 600 5.9 12.91890 15 1-2  2-29 610 5.5 14.0 1440 16 1-8  610 6.3 12.2 1440 17 1-11610 5.4 14.1 1440 18 1-15 610 5.9 12.9 2400 19 1-44 610 6.2 12.3 1680 201-45 610 6.1 12.6 2160 21 1-68 610 6.1 12.7 1680

TABLE 2 1st host 2nd host Luminous Luminance compound compound LuminanceVoltage efficiency half-time Comp. Ex. No. No. (cd/m²) (V) (lm/W) (h) 11-2  — 410 6.2 8.3 430 2 1-8  — 410 7.1 7.2 430 3 1-11 — 410 6.0 8.6 4304 1-15 — 410 7.0 7.4 630 5 1-44 — 420 6.9 7.6 490 6 1-45 — 410 7.4 6.9630 7 1-68 — 420 8.3 6.4 490 8 — 2-1  410 5.9 8.7 700 9 — 2-18 410 6.08.6 630 10 — 2-29 410 7.6 6.8 560

A comparison between Table 1 and Table 2 shows that Examples 1 to 21 hadimproved luminance and lifetime characteristics, and exhibited excellentcharacteristics.

Example 22

A thin film was laminated by a vacuum deposition method at a degree ofvacuum of 4.0×10⁻⁴ Pa on a glass substrate having formed thereon ananode comprising indium tin oxide (ITO) having a thickness of 150 nm.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 20 nm to serve as a hole-injecting layer on the ITO. Next,NPB was formed into a layer having a thickness of 20 nm to serve as ahole-transporting layer. Next, compound 1-2 serving as a first host,compound 2-1 serving as a second host for a light-emitting layer, andtris(2-phenylpyridine)iridium (III) (Ir(PPy)₃) serving as alight-emitting layer guest were co-deposited from different depositionsources to form a light-emitting layer having a thickness of 30 nm. Atthis time, a vapor deposition rate ratio among the first host, thesecond host, and Ir(PPy)₃ was 47:47:6. Next, aluminum (III)bis(2-methyl-8-quinolinato)-4-phenylphenolate (BAlq) was formed into alayer having a thickness of 10 nm to serve as a hole-blocking layer.Next, Alq₃ was formed into a layer having a thickness of 40 nm to serveas an electron-transporting layer. Further, lithium fluoride (LiF) wasformed into a layer having a thickness of 0.5 nm to serve as anelectron-injecting layer on the electron-transporting layer. Finally, Alwas formed into a layer having a thickness of 100 nm to serve as acathode on the electron-injecting layer to produce an organic EL device.

An external power source was connected to the resultant organic ELdevice and a DC voltage was applied to the device. As a result, anemission spectrum having a local maximum wavelength of 517 nm wasobserved and it was found that light emission from Ir(PPy)₃ wasobtained. Table 2 shows the properties (luminance, voltage, luminanceefficiency, and luminance half-time) of the produced organic EL device.

Examples 23 to 42

Organic EL devices were each produced in the same manner as in Example22 except that in Example 22, a compound shown in Table 2 was used asthe first host of the light-emitting layer (Examples 23 to 28).

Organic EL devices were each produced in the same manner as in Examples22 to 28 except that compound 2-18 or 2-29 was used as the second hostof the light-emitting layer (Examples 29 to 42).

An external power source was connected to the resultant organic ELdevices, and a DC voltage was applied to the devices. As a result, anemission spectrum having a local maximum wavelength of 517 nm wasobserved and it was found that light emission from Ir(PPy)₃ wasobtained. Table 3 shows the properties of the produced organic ELdevices.

Comparative Examples 11 to 20

Organic EL devices were each produced in the same manner as in Example22 except that in Example 22, a compound shown in Table 2 was used aloneas the light-emitting layer host. The host amount was set to the sameamount as the total of the first host and second host in Example 22, andthe guest amount was the same. A power source was connected to each ofthe resultant organic EL devices and a DC voltage was applied to thedevice. As a result, an emission spectrum having a local maximumwavelength of 517 nm was observed for each of the organic EL devices andit was found that light emission from Ir(PPy)₃ was obtained. Table 4shows the properties of the produced organic EL devices.

In Tables 3 and 4, the luminance, the voltage, and the luminous efficacyare values at a driving current of 20 mA/cm², and the luminancehalf-time is a value at an initial luminance of 1,000 cd/m².

TABLE 3 1st host 2nd host Luminous Luminance compound compound LuminanceVoltage efficiency half-time Example No. No. (cd/m²) (V) (lm/W) (h) 221-2  2-1  8900 4.2 33.1 12000 23 1-8  8900 4.2 33.5 12000 24 1-11 90004.2 33.3 12000 25 1-15 8900 4.2 33.4 20000 26 1-44 8900 4.2 33.2 1400027 1-45 8900 4.3 32.8 18000 28 1-68 9000 4.3 33.2 14000 29 1-2  2-188700 4.2 32.2 10800 30 1-8  8700 4.2 32.6 10800 31 1-11 8800 4.3 32.410800 32 1-15 8700 4.2 32.5 18000 33 1-44 8700 4.2 32.3 12600 34 1-458700 4.3 32.0 16200 35 1-68 8800 4.3 32.4 12600 36 1-2  2-29 9000 4.233.5 9600 37 1-8  9000 4.2 33.9 9600 38 1-11 9100 4.2 33.7 9600 39 1-159000 4.2 33.8 16000 40 1-44 9000 4.2 33.5 11200 41 1-45 9100 4.3 33.614400 42 1-68 9100 4.3 33.6 11200

TABLE 4 1st host 2nd host Luminous Luminance compound compound LuminanceVoltage efficiency half-time Comp. Ex. No. No. (cd/m²) (V) (lm/W) (h) 111-2  — 7600 4.7 25.6 1810 12 1-8  — 7700 5.2 23.0 1810 13 1-11 — 75004.5 26.2 1810 14 1-15 — 7600 5.1 23.6 2700 15 1-44 — 7600 4.8 25.2 210016 1-45 — 7600 4.4 27.2 2700 17 1-68 — 7500 4.4 26.7 2100 18 — 2-1  76004.5 26.8 3000 19 — 2-18 7500 4.5 26.4 2700 20 — 2-29 7700 5.1 23.7 2400

A comparison between Table 3 and Table 4 shows that Examples 22 to 42had improved luminance and life characteristics, and exhibited excellentcharacteristics.

Example 43

A thin film was laminated by a vacuum deposition method at a degree ofvacuum of 2.0×10⁻⁵ Pa on a glass substrate having formed thereon ananode comprising indium tin oxide (ITO) having a thickness of 70 nm.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 30 nm to serve as a hole-injecting layer on the ITO. Next,NPD was formed into a layer having a thickness of 15 nm to serve as ahole-transporting layer. Next, mCBP serving as a host material for thelight-emitting layer and FIrpic serving as a dopant were co-depositedfrom different deposition sources onto the hole-transporting layer toform a light-emitting layer having a thickness of 30 nm. Theconcentration of FIrpic was 20 wt %. Next, compound 1-15 (compound A)and compound 2-1 (compound B) were co-deposited from differentdeposition sources onto the light-emitting layer to form a hole-blockinglayer having a thickness of 5 nm. At this time, a vapor deposition rateratio of compound 1-15 to compound 2-1 was 50:50 (by weight). Next, Alq₃was formed into a layer having a thickness of 20 nm to serve as anelectron-transporting layer. Further, LiF was formed into a layer havinga thickness of 1.0 nm to serve as an electron-injecting layer on theelectron-transporting layer. Finally, Al was formed into a layer havinga thickness of 70 nm to serve as an electrode on the electron-injectinglayer.

The resulting organic EL device has a layer construction comprising theelectron-injecting layer added between the cathode and theelectron-transporting layer, and the hole-blocking layer added betweenthe light-emitting layer and the electron-transporting layer in theorganic EL device illustrated in FIG. 1. An external power source wasconnected to the resultant organic EL device and a DC voltage wasapplied to the device. As a result, an emission spectrum having a localmaximum wavelength of 475 nm was observed and it was found that lightemission from FIrpic was obtained. Table 5 shows the properties of theproduced organic EL device.

Examples 44 to 48

Organic EL devices were each produced in the same manner as in Example43 except that compound 2-18 or 2-29 was used in place of compound 2-1in Example 43 as compound B for the hole-blocking layer (Examples 44 and45).

Organic EL devices were each produced in the same manner as in Example43 to 45 except that compound 1-15 was used in place of compound 1-45 ascompound A for the hole-blocking layer (Examples 46 to 48).

An external power source was connected to each of the resultant organicEL devices and a DC voltage was applied to the device. As a result, anemission spectrum having a local maximum wavelength of 475 nm wasobserved for each of the organic EL devices and it was found that lightemission from FIrpic was obtained. Table 5 shows the properties of eachof the produced organic EL devices.

Comparative Example 21

An organic EL device was produced in the same manner as in Example 43 inthe film thickness of Alq₃ serving as the electron-transporting layer inExample 43 was 25 nm and no hole-blocking layer was provided.

In Table 5, the luminance, the voltage, and the luminous efficacy arevalues at a driving current of 2.5 mA/cm², and the luminance half-timeis a value at an initial luminance of 1,000 cd/m².

TABLE 5 Compound Compound Luminous Luminance A B Luminance Voltageefficiency half-time Example No. No. (cd/m²) (V) (lm/W) (h) 43 1-15 2-1 620 6.1 12.7 1500 44 2-18 600 6.9 10.8 1350 45 2-29 590 5.0 14.9 1200 461-45 2-1  620 7.0 11.0 1500 47 2-18 580 7.2 10.0 1500 48 2-29 590 6.211.9 1050 Comp. Ex. 21 — — 520 9.4 7.0 300

Table 5 shows that Example 43 to 48 comprising two compounds used forthe hole-blocking layer exhibited excellent characteristics, as comparedto Comparative Example 21 comprising no hole-blocking material.

INDUSTRIAL APPLICABILITY

The organic EL device of the present invention has high luminousefficacy at a low driving voltage and a long life, and is expected to beapplied to full-color or multi-color panels. The organic EL device ofthe present invention can be used for mobile device displays, and alsocan be used for organic EL displays or organic EL lighting devices of TVsets or automobiles.

REFERENCE SIGNS LIST

-   1 substrate-   2 anode-   3 hole-injecting layer-   4 hole-transporting layer-   5 light-emitting layer-   6 electron-transporting layer-   7 electron-injecting layer-   8 cathode

1. An organic electroluminescent device comprising a substrate havingstacked thereon an anode, organic layers, and a cathode, wherein atleast one layer of the organic layers comprises (i) a compoundrepresented by the following general formula (1) and (ii) a compoundrepresented by the following general formula (2):

wherein L¹ is a substituted or unsubstituted p-valent aromatichydrocarbon group having 6 to 30 carbon atoms, substituted orunsubstituted a p-valent heteroaromatic ring group having 3 to 30 carbonatoms other than a carbazolyl group, or a p-valent linked aromatic groupobtained by linking 2 to 6 aromatic rings of the substituted orunsubstituted aromatic rings, each R independently represents hydrogen,a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30carbon atoms, a substituted or unsubstituted heteroaromatic ring grouphaving 3 to 30 carbon atoms other than a carbazolyl group, a linkedaromatic group obtained by linking 2 to 6 aromatic rings of thesubstituted or unsubstituted aromatic hydrocarbon groups orheteroaromatic ring groups, a linear, branched, or cyclic alkyl grouphaving 1 to 12 carbon atoms, a diarylamino group having 12 to 44 carbonatoms, a cyano group, a nitro group, or a fluoro group, p is asubstitution number and represents an integer of 1 to 3, m is arepeating number, and each m is independently an integer of 2 to 4,

wherein ring A is a divalent carborane group of C₂B₁₀H₁₀ represented byformula (a1) or formula (b1), with the proviso that when a plurality ofrings A are present in a molecule, the plurality of rings A may be thesame or different from each other; q is a substitution number and is aninteger of 1 to 4; n is a repeating number and is an integer of 0 to 2;L² represents a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 carbon atoms, a substituted or unsubstitutedheteroaromatic ring group having 3 to 30 carbon atoms, or a linkedaromatic group obtained by linking 2 to 6 aromatic rings of thesubstituted or unsubstituted aromatic hydrocarbon groups orheteroaromatic ring groups, L³ represents a single bond, a substitutedor unsubstituted (q+1)-valent aromatic hydrocarbon group having 6 to 30carbon atoms, a substituted or unsubstituted (q+1)-valent heteroaromaticgroup having 3 to 30 carbon atoms, or a (q+1)-valent linked aromaticgroup obtained by linking 2 to 6 aromatic rings of the substituted orunsubstituted aromatic hydrocarbon groups or heteroaromatic ring groups,with the proviso that when q=1 and n=1, L³ represents a single bond, aheteroaromatic ring group, or a linked aromatic group comprising atleast one heteroaromatic ring group, and L⁴ independently represents asingle bond, a substituted or unsubstituted divalent aromatichydrocarbon group having 6 to 30 carbon atoms, a substituted orunsubstituted divalent heteroaromatic ring group having 3 to 30 carbonatoms, or a substituted or unsubstituted linked aromatic group obtainedby linking 2 to 6 aromatic groups of the aromatic hydrocarbon groups orthe heteroaromatic ring groups.
 2. The organic electroluminescent deviceaccording to claim 1, wherein, in general formula (1), p is an integerof 1 or 2, m is independently an integer of 2 or 3, and all bindingstructures between carbazolyl groups are represented by formula (d1) orboth of formula (c1) and formula (d1).

wherein R is the same as in general formula (1).
 3. The organicelectroluminescent device according to claim 2, wherein, in generalformula (1), all binding structures between carbazolyl groups arerepresented by both of formula (c1) and formula (d1).
 4. The organicelectroluminescent device according to claim 1, wherein, in generalformula (1), L¹ is a p-valent group formed by removing p hydrogen atomsfrom any one of formulae (3) to (6).

in formulae (3) to (6), each X independently represents CH or nitrogen,each R′ independently represents hydrogen, a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted heteroaromatic ring group having 3 to 30carbon atoms, an alkyl group having 1 to 12 carbon atoms, a diarylaminogroup having 12 to 44 carbon atoms, a cyano group, a nitro group, or afluoro group; in formulae (4) and (6), Y represents oxygen or sulfur,and in formulae (5), r represents an integer of 0 to
 2. 5. The organicelectroluminescent device according to claim 4, wherein, in generalformula (1), L¹ is a p-valent group formed by removing p hydrogen atomsfrom any one of formulae (3), (4), and (5).
 6. The organicelectroluminescent device according to claim 1, wherein, in generalformula (1), the total of m is an integer of 2 to
 6. 7. The organicelectroluminescent device according to claim 1, wherein, in generalformula (2), ring A is a divalent carborane group of C₂B₁₀H₈ representedby formula (a1).
 8. The organic electroluminescent device according toclaim 1, wherein, in general formula (2), aromatic rings of L² and L³,which directly bond to ring A, are the same.
 9. The organicelectroluminescent device according to claim 1, wherein, in generalformula (2), L² and L³ are a substituted or unsubstituted dibenzofuranylgroup or a substituted or unsubstituted dibenzothiophenyl group.
 10. Theorganic electroluminescent device according to claim 1, wherein anorganic layer comprising a compound represented by general formula (1)and a compound represented by general formula (2) is at least one layerselected from the group consisting of a light-emitting layer containinga luminescent dopant, an electron-blocking layer, and a hole-blockinglayer.
 11. The organic electroluminescent device according to claim 10,wherein the organic layer is a light-emitting layer containing aluminescent dopant and comprises a compound represented by generalformula (1) and a compound represented by general formula (2) as hostmaterials.
 12. The organic electroluminescent device according to claim11, wherein the luminescent dopant is a delayed fluorescent dopant. 13.The organic electroluminescent device according to claim 11, theluminescent dopant is an organometallic complex comprising at least onemetal selected from ruthenium, rhodium, palladium, silver, rhenium,osmium, iridium, platinum, and gold.
 14. The organic electroluminescentdevice according to claim 4, wherein an organic layer comprising acompound represented by general formula (1) and a compound representedby general formula (2) is at least one layer selected from the groupconsisting of a light-emitting layer containing a luminescent dopant, anelectron-blocking layer, and a hole-blocking layer.